Locustella Warblers

“What’s your favourite bird?” has to be one of the most frequently asked questions that birders receive. Personally, it’s impossible for me to choose just one bird. I can tell which groups of birds are my favourites though, and Locustella warblers are one of them. I instantly fell in love with these mouse-like birds when I first saw them sneaking mousily through the thick covered ground. I’ve always been keen to see as many of them as possible ever since. In this post, I’d like to share what I’ve gathered so far about all the Locustella warblers in Thailand.

There are 6 species in the genus Locustella that have been recorded in Thailand. These include 1) Lanceolated Warbler (L. lanceolata), 2) Brown Bush Warbler (L. luteoventris), 3) Chinese Bush Warbler (L. tacsanowskia), 4) Baikal Bush Warbler (L. davidi), 5) Spotted Bush Warbler (L. thoracica), and 6) Russet Bush Warbler (L. mandelli). Through this post, I’ll share my photos and notes about each species in that order.

Lanceolated Warbler is the most abundant and widespread Locustella warbler in Thailand. It can be found in dry grassy habitats throughout the country in winter months. During passage migration, particularly in spring, it is also found in urban parks and on offshore islands. It is the easiest one to identify as well, with its well streaked plumage unlike any other species recorded in Thailand (unless someone finds the Common Grasshopper Warbler; L. naevia!). Once you learn its insect-like calls, you’d realise how common it is. I’m still intrigued by its plumage variation though. Some birds can have very bold streaking on the plumage, while some appear much plainer.

Lanceolated Warbler — the crown and breast is finely streaked
Lanceolated Warbler — a different bird with bolder streaking

Brown Bush Warbler is possibly the rarest (if not overlooked) member of the genus Locustella in Thailand. I’ve only heard its very unusual song a few times on Doi Angkhang and Doi Lang in spring. So far, I’ve only been able to photograph it once when I found a singing male at Doi Lang (east) on 22 April 2012. Its seasonal status is still somewhat uncertain, and is still assumed to be a non-breeding visitor. All records so far came from grassy patches on high mountains in the northwest.

Here’s a video of the singing bird that I found in 2012. It’s quite hard to believe that’s a bird song!
Brown Bush Warbler — note the overall warm rufescent-brown plumage with long tail and warm brownish undertail coverts. The bill base is yellowish even in breeding season.

Chinese Bush Warbler is another rare Locustella warbler in Thailand. It is a non-breeding visitor that can be found in the northwest during winter. It seems to prefer dry and degraded habitats in lowland and foothills where birders don’t normally visit. In recent years, it has been seen quite regularly in grassy patches and cultivated area (mostly corn plantation) near Takkataen Cave in Ob Khan National Park, Chiang Mai. It is still an extremely difficult bird to see though. During winter, it seems to be much shyer than most Locustella warblers, and rarely allows a full view in the open. It is the only species that I’ve yet to obtain a decent photo. Although looking nearly identical to the Brown Bush Warbler, this species has whitish undertail coverts with very faint brownish markings as shown in the photo above.

Baikal Bush Warbler is the secondmost abundant and widespread Locustella warbler in Thailand. It can be found in reed beds and wetlands throughout much of Thailand during winter months, except south of the Kra Isthmus. It has an incredible plumage variation that often confuses birders. The most unique features of this species include the rather short tail with bold white scallops on the undertail coverts. It can sometimes shares the same habitat with the Lanceolated Warbler, but usually prefers wetter areas.

Baikal Bush Warbler — the typical look; note the short tail and bold white scallops on undertail coverts
Baikal Bush Warbler — a brown morph lacking grey wash on the cheeks and breast; the black spotting on the upper breast is also extremely variable
Baikal Bush Warbler — this individual lacks any black spotting on the upper breast
Baikal Bush Warbler — in spring, they go through a major moult of wing and tail feathers, and might easily confuse birders

Spotted Bush Warbler is another rare Locustella warbler in Thailand. There are only few confirmed records of this winter migrant from the northwest. It seems to share the same habitats with the more common Baikal Bush Warbler, preferring wetlands and reed beds. Identification of the 2 species can be extremely challenging. Generally speaking, the Spotted Bush Warbler is larger with longer tail, and less white on the undertail coverts, but these are all very difficult to judge. The best way to confirm the identification is by hearing the song. The Spotted Bush Warbler has a melodic song unlike the song of Baikal Bush Warbler which is a monotonic “dzeep”. I find that even in winter, both species still erratically sing their songs or sub-songs, particularly in early morning. I would not claim a Spotted Bush Warbler with certainty without hearing the song or measuring it in-hand.

Spotted Bush Warbler — confirmed by song; note the long tail compared to Baikal Bush Warbler
A video captured by Watanawong Wongpan confirms that the bird that I found at Nam Kham Nature Reserve in spring of 2016 was indeed a Spotted Bush Warbler when it briefly sang while preening.
Spotted Bush Warblerconfirmed by song; a brown morph without grey wash on the cheeks and breast nor black spotting on the upper breast

Russet Bush Warbler is the only Locustella warbler that is known to breed in Thailand so far. It is quite uncommon in general, but can be locally common in suitable habitat. This species prefers open grassland and degraded forest edge on high mountains. It is known to breed in the northwest, and occurs as far south as Kamphaengphet-Tak province. Despite being a breeding bird that can be frequently heard in summer and wet season, I find it to be one of the most difficult Locustella warblers to see well. It is extremely shy and secretive, and rarely strays away from the dense vegetation even while singing. Unlike most Locustella warblers, the Russet Bush Warbler sings from the thickest part of the vegetation, not from the top of it. With lots of effort invested, I could finally get some decent photos of this shy bird earlier this year.

Russet Bush Warbler — typically sings from the thickest part of the vegetation
A Russet Bush Warbler singing its unique insect-like song.
Russet Bush Warbler — note the very long tail and black bill (in breeding season). The plumage is extremely variable. The breast can be either greyish or brownish, with or without black spotting on the upper breast.
Russet Bush Warbler — one of the most misleading characteristics depicted in most guide books is pattern of the undertail coverts. Most illustrations show brownish undertail coverts with well marked whitish tips (scallops) similar to those of the Spotted/Baikal Bush Warbler. In reality, the undertail coverts usually appear poorly marked, if not, plain brownish, as shown in this picture.

4 thoughts on “Locustella Warblers

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  1. Russet Bush Warbler has a unique black bill and long tail, so I am surprised. The videos also enable me to compare your local warblers’ singing with that of neighborhood warblers here – Japanese Bush and Eurasian Reed Warblers. Thanks!

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